Oxidative DMA Damage and Genetic Instability in Models of Intestinal Tumor Development It is well-established that oxidative DMA damage can cause mutations that have been implicated in tumor development. During the previous program project support period, we exploited isogenic yeast strains to determine the relationships between those pathways involved in removal/repair of oxidative DMA damage and those pathways that tolerate its presence in the genome via DNA polymerase-mediated translesion synthesis and recombination leading to genetic instability. In addition, we have established that the chronic presence of unrepaired DNA damage causes a "stress adaptation" response that leads to an increase in intracellular ROS accompanied by further increases in genetic instability and a host of physiological changes similar to the cancer cell phenotype. In project 2, we will further define the relevance of the DNA damagemediated ROS/genetic instability response within the context of it being a driver of small- and large-scale genomic rearrangements in both yeast and mammalian cells. We will also determine the relationships among oxidative DNA damage, DNA repair and genetic instability activities during various stages of tumor development in a mouse colon cancer system where mitochondrial- and Nox-mediated generators of ROS have been activated. We will also continue our collaborative studies to further elucidate the connections between oxidative mtDNA damage, mtDNA genetic instability and those systems that respond (or fail to respond) to such damage. The specific aims of this project are designed to exploit yeast to rapidly identify key ROS mediators of genetic instability and to define the nature of abnormal chromosomal changes caused by ROS as a result of DNA damage caused by exogenous and endogenous agents. The results of the yeast studies will be used to focus attention on similar relationships that we hypothesize will exist during the development of mammalian colon tumors where increasing intracellular ROS functions as a driver (via oxidative DNA damage) of small- and large-scale genomic changes, from point mutations to chromosomal aberrations, including amplifications, deletions, and non-reciprocal translocations. The results of these studies should provide a picture of the extent to which ROS functions as the mediator of genetic instability during colon tumor development in mammalian intestinal cells.